Active seat belt control system with built in interia sensor

ABSTRACT

Control system for controlling the locking and unlocking of seat belt retractors in response to the opened/closed state of the vehicle doors and also the on/off state of the ignition switch.

FIELD OF THE INVENTION

The present invention generally relates to an active seat belt controlsystem for controlling the locking and unlocking of seat belt retractorsin a vehicle, and more particularly, relates to an active seat beltcontrol system for controlling the locking and unlocking of seat beltretractors in a vehicle incorporating a logic and timer circuit with abuilt-in inertia sensor.

BACKGROUND OF THE INVENTION

Safety seat belt systems have been used in motor vehicles for manyyears. Traditionally, active seat belt systems have been used thatrequire the occupant to actively participate in securing the belt andproviding a safe driving environment. More recently, passive seat beltsystems have also been used in the automotive industry which do notrequire the vehicle occupant to actively participate in securing thebelt. Instead, a seat belt is automatically fastened around the occupantwhen he is in a seated position. This type of passive seat belt systemhas caused some degree of inconvenience to the drivers and passengersalike and consequently, has met considerable consumer resistance inusing such passive systems. As a consequence, a combination of an activeseat belt system and a passive restraint system (such as airbags) hasbeen employed by many automobile manufacturers. This combinationprovides the convenience of an active seat belt system while stillproviding maximum protection when used with airbags.

In a conventional active seat belt system, an inertia sensor is used asan impact sensor and is mechanically linked to the seat belt retractionsystem. When the vehicle experiences a sudden deceleration, accelerationor sharp cornering, the inertia sensor senses such sudden motion andlocks the seat belt retractor thereby retaining the seat belts securelyon the driver or passenger. In more recent vehicle interior designs,seat belts are frequently integrated into the vehicle seat and mountedtherein with a seat belt retractor.

This type of integrated vehicle seat/seat belt system is also desirablefor vehicles equipped with convertible roofs. In these vehicles, theseat belt and the seat belt retraction system are mounted in the seatsince there is no convenient pillar for mounting the turning loop. Insome convertible vehicles, the seat belt retractor is mounted in thelower part of the vehicle body and the seat belt extends from theretractor, over the shoulder of the vehicle seat, through a harness anddown to the lower part of the vehicle body. This design can causediscomfort to the seat belt wearer.

When a seat belt and a seat belt retraction system are mounted in theupper part of the vehicle seat, the inertia sensor which is normallymounted to the seat belt retractor can no longer be mounted togetherwith the retractor. This is because the seat back of a vehicle seat isfrequently tilted or reclined by a driver or a passenger for optimumcomfort. In such applications, the change in orientation of the inertiasensor must be accounted for in order for the inertia sensor to operateproperly. It is therefore desirable to mount the inertia sensor remotelyfrom the seat belt retractor when the seat belt retractor is mounted inthe vehicle seat. This type of remotely mounted inertia sensor forcontrolling a seat belt retraction system has been proposed by others.

One of such prior art method proposes mounting of an inertia sensor inthe vehicle floor. In such applications, the inertia sensor functions asan electrical switch. When vehicle electrical current is turned on,current is fed to the system such that when the inertia sensor senses asudden movement of the vehicle, it sends an electrical signal to eitherturn on or turn off a solenoid. The solenoid deactivates the seat beltretractor and locks the belt. One problem with such a system is thatprior to the ignition switch being turned on, the seat belt retractionsystem is locked and as a consequence, the belt cannot be fastened bythe driver or the front seat passenger of the vehicle. This type ofignition switch activated seat belt system is inconvenient. Forinstance, when the driver opens the vehicle door to fasten a child seat,the seat belt cannot be extended unless the ignition switch is alreadyturned on. Furthermore, as soon as the ignition switch is turned off,the seat belt retractor is locked preventing any movement of the seatbelt. This is inconvenient if the driver is still strapped in the seatbelt. For instance, his motion will be restricted and he is preventedfrom reaching out and picking up personal item (e.g. an umbrella) fromthe floor area of the passenger seat.

It is therefore an object of the present invention to provide an activeseat belt control system that can be mounted remotely from the vehicleseat to control the locking and unlocking of the seat belt retractionsystem.

It is another object of the present invention to provide an active seatbelt control system that is remotely mounted from the vehicle seat thatis not solely controlled by the vehicle ignition switch.

It is a further object of the present invention to provide an activeseat belt control system that incorporates a logic circuit such that theseat belt retraction system is operable prior to and after the ignitionswitch is turned on or off.

It is yet another object of the present invention to provide an activeseat belt control system that is remotely mounted from the vehicle seatand controlled by a logic and timer circuit equipped with a built-ininertia sensor.

SUMMARY OF THE INVENTION

In accordance with the present invention, an active seat belt controlsystem for controlling the locking and unlocking of the seat beltretractors in a vehicle incorporating a timer and a logic circuit isprovided.

In the preferred embodiment, an active seat belt control system isprovided that operates electronically and is used to replace aconventional system that operates mechanically. A solenoid is mountedwith the seat belt retractor in the upper portion of the vehicle seat toperform the locking and unlocking function when a signal is receivedfrom an inertia sensor through the seat belt control system. The inertiasensor is remotely mounted at a convenient location inside a logic andtimer module. The solenoid is equipped with a lever arm to engage gearswhich in turn lock or unlock the seat belt retractor. The presentinvention enables a vehicle designer to mount an inertia sensor in aremote location from the vehicle seats such that the seat movement doesnot affect the operation of the seat belt control system. A singleinertia sensor can be used to control the seat belt retractor systemsfor both the front seats.

The preferred embodiment provides an electronic logic and timer circuitthat includes a built-in inertia sensor. The timer circuit is triggeredindirectly by a detection means responsive to the opening and closing ofthe vehicle doors wherein the detection means generates an output signalindicating a change in status of the doors. For instance, when a dooropening signal is received by the logic circuit, the seat belt retractorremains unlocked for a predetermined period of time. If during that timethe ignition switch of the vehicle is turned on, the seat belt retractorwill remain unlocked (for as long as the ignition switch is turned on)unless the inertia sensor senses a sudden deceleration of the vehicle.When the ignition switch of the vehicle is turned off, the ignitionswitch sends a signal to the timer which in turn provides current to thesolenoid and continues to deactivate the locking system of the seat beltretractor for a predetermined period of time. During such period oftime, the seat belt wearer can freely move without being restrained by alocked seat belt.

The preferred embodiment further includes a built-in inertia sensorincorporated into the logic/timer circuit module to achieve a morereliable, a faster responding and a more serviceable system.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects, features and advantages of the present invention willbecome apparent upon consideration of the specification and the appendeddrawings, in which:

FIG. 1 is a general electrical block diagram of the active seat beltcontrol system of the present invention.

FIG. 2 is a logic flow diagram of the active seat belt control system ofFIG. 1.

FIG. 3 is a circuit diagram of the seat belt control systemincorporating a built-in inertia sensor.

FIG. 4 is a functional block diagram of IC1 through IC5.

FIG. 5A through 5G are timing diagrams showing the signal timing for theseat belt control system of FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention utilizes an electronic active seat belt controlsystem incorporating a logic and timer circuit equipped with a built-ininertia sensor to replace a mechanical/electrical seat belt controlsystem.

In the preferred embodiment, the present invention supplants an inertiasensor that is commonly used in a seat belt retractor mechanism with asolenoid such that the locking and unlocking of the retractor iscontrolled electronically and not mechanically. The electronicallycontrolled solenoid is equipped with a lever arm to engage or disengagea set of gears thus locking or unlocking the seat belt retractionsystem. Utilizing this design, the inertia sensor can be mounted at aremote location away from the vehicle seat and as a consequence, theseat orientation does not affect the operation of the inertia sensor.Furthermore, only one inertia sensor is needed to control the seat beltretractors in both the driver's and the passenger's seats. The inertiasensor can be suitably mounted on the vehicle floor between the frontseats. The inertia sensor senses a preset level of deceleration oracceleration with a 360° range of sensitivity and interrupts the currentto the solenoids thereby locking the seat belt retractors.

The present invention further incorporates a timer that is activated bya change in door status. This enables the solenoids to unlock theretractor systems, for a preset length of time before the ignitionswitch is turned on. More specifically, the system is connected to adoor ajar switch which is activated when the vehicle door is opened. Thetimer starts when the door is opened to allow the driver or passengerfor a predetermined length of time to pull on the seat belt and tofasten it before the ignition switch is turned on. This timer systemalso allows for a preset length of time during which the solenoidsremain energized after the ignition switch is turned off. This isaccomplished by utilizing a detection system that monitors the ignitionswitch state. For instance, the system is connected to the ignitionswitch and is activated when the ignition is turned off. The timerstarts when the ignition is turned off to allow the retractors to remainunlocked for a predetermined length of time.

The present system therefore is much easier to use and moreuser-friendly than conventional systems wherein the seat belt cannot beused until the ignition switch is turned on. In such conventionalsystems, the inertia sensor receives its power directly from theignition switch in order to turn power on or off to the solenoids. Whenthe ignition switch is off, no power is supplied to the solenoids andthe seat belt retractors are locked and inoperative.

Another benefit provided by the present invention is that the seat beltsremain operative after the ignition switch is turned off. This iscontrary to those conventional seat belt control system in which theseat belt retractor is locked as soon as the ignition switch is turnedoff. The present invention therefore provides the additional convenienceto a driver or passenger for a predetermined length of time by keepingthe solenoids powered thereby allowing seat belt movement after theignition switch is turned off. The operation of the timer is alsocontrolled by the ignition switch. Whenever the state of the ignitionswitch changes from on to off, the timer enables current to flow to thesolenoids for a predetermined period of time. The solenoids stay poweredduring that time and allow the retraction and extension of the seatbelts.

The present invention also provides an additional safety factor bylocking the seat belt retractor systems whenever power to the system isinterrupted. For instance, when the vehicle is involved in a collisionand the power to the solenoids is interrupted, the seat belt retractorsare locked to safely restrain the driver and the passenger in theirseats.

Referring to FIG. 1 where a general block diagram of the active seatbelt control system of the present invention is shown, logic and timercircuit 10 (or L/T circuit 10) requires an input from the ignitionswitch 12, the battery 14, the right door ajar switch 18, the left doorajar switch 16, and the ground 20. The output from the L/T circuit 10 istransferred to inertia sensor 22. The output of inertia sensor 22 isconnected to a pair of solenoids 24 and 26 for activating the seat beltlocking mechanisms for the driver and passenger seat respectively.

The L/T circuit 10 preferably utilizes a voltage output equal inpotential to that of the vehicle battery for controlling the solenoids.This is shown in FIG. 1 where 12 volts from battery 14 is used to powerL/T circuit 10, the inertia sensor 22, and to drive solenoids 24 and 26.Driving the solenoids with 12 volts provides a safety benefit to thesystem. For instance, if the electrical wiring system fails, it is muchsafer for the seat belt wearers if the solenoids operate on high voltagebecause any grounding of the 12 volt line between L/T circuit 10 andlatch mechanisms 24, 26 is readily detachable (the retractors wouldlock). In a low voltage system this may not be the case.

The logic employed by the seat belt control system is discussed below.Now referring to FIG. 2, if the vehicle is presently in a quickdeceleration node 30 or the vehicle is parked on a steep incline 38(e.g. ±12 degrees), the seat belt retractors should be locked (i.e. theseat belt wearers are restrained). However, if the answers to questionblocks 30 and 38 are no, and if one or more of the following is true:

(1) the key is in the run or the accessory position 44, or

(2) a door has been opened or closed within the past five minutes 52, or

(3) the key has been moved to the off or lock position within the pastfive minutes 58,

then the retractor should be unlocked 48. If neither (1), (2), or (3)above can be answered in the affirmative, then the retractors arelocked. This third scenario (i.e. the key has been moved to the offposition within the past five minutes) anticipates the case where thedriver is waiting for someone. And, if this waiting does not extendbeyond a 5 minute time period, the seat belt retractors should remainunlocked.

The L/T 10 circuit is designed to receive inputs from the driver doorajar switch, the passenger door ajar switch, and the ignition switch.The system of the present invention recognizes the status of theseswitches and generate the appropriate response for each condition (seeTable 1).

                                      TABLE 1                                     __________________________________________________________________________    Inputs  Driver's Door                                                                           Passenger Door                                                                          Outputs                                           Ignition                                                                              WAS changed TO                                                                          WAS changed TO                                                                          Restraint                                         __________________________________________________________________________     1.                                                                             Off   Open Open Open Open No change                                          2.                                                                             Off   Open Open Open Close                                                                              Power xx min.                                      3.                                                                             Off   Open Open Close                                                                              Open Power xx min.                                      4.                                                                             Off   Open Open Close                                                                              Close                                                                              No change                                          5.                                                                             Off   Open Close                                                                              Open Open Power xx min.                                      6.                                                                             Off   Open Close                                                                              Open Close                                                                              Power xx min.                                      7.                                                                             Off   Open Close                                                                              Close                                                                              Open Power xx min.                                      8.                                                                             Off   Open Close                                                                              Close                                                                              Close                                                                              Power xx min.                                      9.                                                                             Off   Close                                                                              Open Open Open Power xx min.                                     10.                                                                             Off   Close                                                                              Open Open Close                                                                              Power xx min.                                       Off   Close                                                                              Open Close                                                                              Open Power xx min.                                       Off   Close                                                                              Open Close                                                                              Close                                                                              Power xx min.                                       Off   Close                                                                              Close                                                                              Open Open No change                                           Off   Close                                                                              Close                                                                              Open Close                                                                              Power xx min.                                       Off   Close                                                                              Close                                                                              Close                                                                              Open Power xx min.                                       Off   Close                                                                              Close                                                                              Close                                                                              Close                                                                              No change                                           On    Open Open Open Open Constant power                                      On    Open Open Open Close                                                                              Constant power                                      On    Open Open Close                                                                              Open Constant power                                    20.                                                                             On    Open Open Close                                                                              Close                                                                              Constant power                                      On    Open Close                                                                              Open Open Constant power                                      On    Open Close                                                                              Open Close                                                                              Constant power                                      On    Open Close                                                                              Close                                                                              Open Constant power                                      On    Open Close                                                                              Close                                                                              Close                                                                              Constant power                                      On    Close                                                                              Open Open Open Constant power                                      On    Close                                                                              Open Open Close                                                                              Constant power                                      On    Close                                                                              Open Close                                                                              Open Constant power                                      On    Close                                                                              Open Close                                                                              Close                                                                              Constant power                                      On    Close                                                                              Close                                                                              Open Open Constant power                                    30.                                                                             On    Close                                                                              Close                                                                              Open Close                                                                              Constant power                                      On    Close                                                                              Close                                                                              Close                                                                              Open Constant power                                      On    Close                                                                              Close                                                                              Close                                                                              Close                                                                              Constant power                                      On to Off                                                                           Open Open Open Open Power xx min.                                       On to Off                                                                           Open Open Open Close                                                                              Power xx min.                                       On to Off                                                                           Open Open Close                                                                              Open Power xx min.                                       On to Off                                                                           Open Open Close                                                                              Close                                                                              Power xx min.                                       On to Off                                                                           Open Close                                                                              Open Open Power xx min.                                       On to Off                                                                           Open Close                                                                              Open Close                                                                              Power xx min.                                       On to Off                                                                           Open Close                                                                              Close                                                                              Open Power xx min.                                     40.                                                                             On to Off                                                                           Open Close                                                                              Close                                                                              Close                                                                              Power xx min.                                       On to Off                                                                           Close                                                                              Open Open Open Power xx min.                                       On to Off                                                                           Close                                                                              Open Open Close                                                                              Power xx min.                                       On to Off                                                                           Close                                                                              Open Close                                                                              Open Power xx min.                                       On to Off                                                                           Close                                                                              Open Close                                                                              Close                                                                              Power xx min.                                       On to Off                                                                           Close                                                                              Close                                                                              Open Open Power xx min.                                       On to Off                                                                           Close                                                                              Close                                                                              Open Close                                                                              Power xx min.                                       On to Off                                                                           Close                                                                              Close                                                                              Close                                                                              Open Power xx min.                                       On to Off                                                                           Close                                                                              Close                                                                              Close                                                                              Close                                                                              Power xx min.                                       Off to On                                                                           Open Open Open Open Constant power                                    50.                                                                             Off to On                                                                           Open Open Open Close                                                                              Constant power                                      Off to On                                                                           Open Open Close                                                                              Open Constant power                                      Off to On                                                                           Open Open Close                                                                              Close                                                                              Constant power                                      Off to On                                                                           Open Close                                                                              Open Open Constant power                                      Off to On                                                                           Open Close                                                                              Open Close                                                                              Constant power                                      Off to On                                                                           Open Close                                                                              Close                                                                              Open Constant power                                      Off to On                                                                           Open Close                                                                              Close                                                                              Close                                                                              Constant power                                      Off to On                                                                           Close                                                                              Open Open Open Constant power                                      Off to On                                                                           Close                                                                              Open Open Close                                                                              Constant power                                      Off to On                                                                           Close                                                                              Open Close                                                                              Open Constant power                                    60.                                                                             Off to On                                                                           Close                                                                              Open Close                                                                              Close                                                                              Constant power                                      Off to On                                                                           Close                                                                              Close                                                                              Open Open Constant power                                      Off to On                                                                           Close                                                                              Close                                                                              Open Close                                                                              Constant power                                      Off to On                                                                           Close                                                                              Close                                                                              Close                                                                              Open Constant power                                      Off to On                                                                           Close                                                                              Close                                                                              Close                                                                              Close                                                                              Constant power                                    __________________________________________________________________________

The battery input for L/T circuit 10 should correspond to the vehicle'sbattery positive potential and should be capable of handling the currentdelivery requirements of the solenoid outputs. The ground input of theL/T circuit 10 should correspond to the negative potential of thevehicle battery and be capable of handling the current drawn by the L/Tcircuit 10. The ignition input for the module should correspond to thepositive potential of the vehicle battery and should be used to sensethe status of the ignition switch. The door ajar switch should supplyL/T circuit 10 with an open circuit whenever the door is closed and agrounded circuit whenever the door is open.

An examination of Table 1 indicates that when the ignition is off, anychange of the door state (from closed to open or open to closed) ofeither the driver door or the passenger door generates retractor unlocksignal. This is shown in cases 1-16. In cases 17-32 where the ignitionis on, a constant power is supplied (by way of line 109) to thesolenoids to unlock the retractors. This occurs regardless of the doorstate changes. In cases 33-48 where the ignition switch is changed fromon to off, power is supplied to the solenoids for a predetermined amountof time to enable the usage of the seat belts by keeping them in anunlocked position. In cases 49-64 where the ignition switch is changedfrom the off to the on position, a constant power is supplied to thesolenoids unlocking the seat belt retractors.

Table 1 indicates that the outputs are on for "xx min." (i.e. a fixedtime period) whenever either of the door inputs change state (opened toclosed or vice versa) or the ignition input changes from the on to theoff state (i.e, timer starts when a driver or passenger opens or closesa door or turns off the ignition). Fixed time period "xx" is preferablyanywhere between 5-6 minutes. This fixed time cycle can be set for anydesirable amount of time.

Whenever sudden motion is sensed, inertia sensors activate and theretractors are locked. This occurs regardless of the state of any of theinputs shown in FIG. 1.

Referring now to FIG. 3, where a detailed circuit diagram of the activeseat belt control system of the present invention is shown. The T/Lcircuit 10 is preferably constructed using integrated circuit chips(indicated by IC1 through IC5). IC2 is a timer chip while the other 4chips, IC1, IC3, IC4, and IC5 are preferably dual precision,retriggerable/resettable monostable multivibrators (hereinafterone-shots). The timer chip, IC2, is preferably a monolithic timingcircuit capable of producing accurate time delays. The timer canpreferably be triggered and reset on rising or falling signal edges, andthe output of the timer can preferably source or sink up to 200 ma. Sucha timer circuit that is suitable for the present invention is a MotorolaMC1455 chip.

One-shots 100-114 may be configured to trigger from either edge of aninput pulse (but not both), and produce an accurate pulse output over awide range, the duration and the accuracy of which are determined by theexternal timing components (not shown). A typical one-shot that issuitable for the present invention is a Motorola MC14538B integratedcircuit. A functional block diagram of the Motorola MC14538B is shown inFIG. 4.

In the circuit of FIG. 3, one shot 100, is configured to activate itsoutputs 100', 100" on a closed to opened transition of the driver's doorand one shot 102 is configured to activate its output on an opened toclosed transition of the driver's door. Thus one-shots 100 and 102compliment one another in that whenever switch 118 changes state, anoutput signal is present on one of their respective output lines 100'and 102'. The respective outputs 100' and 102' are "hard wire or'ed"together move and present an input trigger signal to timer 116. The samecircuit arrangement is used to sense passenger door change of state andoutputs 104' and 106' are "hard wire-or'ed" together and presented as aninput trigger signal to timer 116. When either of the doors move from aclosed to open position, output signals 100" and 104" are sensed byone-shots 110, 112 respectively, which, in turn reset timer 116. Thisguarantees that timer 116 is reset (regardless of where it is in itscurrent timing cycle) whenever a door status changes so that it canbegin another fixed time cycle (i.e. a fixed time cycle begins each timethe driver or passenger door is closed).

One-shot 108 controls the ignition off signal lines 108' and 108". Line108" sets the timer (i.e. turns the timer on if not already so, but doesnot interfere with its timing cycle if already initiated) for the fixedtime cycle when the ignition switch is turned off. Line 108' functionssimilarly to that of the other one-shots to reset timer 116 (i.e. causesthe timer to initiate a new timing cycle regardless of where it is inthe current timing cycle) when the ignition is turned off. Line 109 runsfrom pin 5 of IC1A to node 117. Line 109 ensures that whenever ignitionis turned on, node 109 is held at 12 volts thus ensuring that the timeris ineffective for locking the retractors while the ignition is on.Transistors Q1-Q9 are used as inverter/drivers in a conventional manner.Diodes, D1-D7 allow current to flow only in one direction.

Now referring to FIGS. 5A through 5G, when the driver door moves from aclosed position to an open position (see FIG. 5A), the voltage at pin 9of one-shot 100 drops to zero for a short period of time (preferably inthe range of 1-100 milliseconds) then rises back to 12 volts (see FIG.5B). The voltage signal at pin 5 of one-shot 110 is shown in FIG. 5E andessentially duplicates the voltage signal of FIG. 5B. The signal shownin FIG. 5E triggers one-shot 110 and causes the output of one-shot 110to generate the signal shown in FIG. 5F. The rising edge of the signalof FIG. 5B triggers timer 116 (see FIG. 5D) thereby setting timer 116 torun for a fixed time. After this fixed time is expired, the output oftimer 116 drops to zero volts causing the seat belt retractors to lock.

In the case where the driver's door experiences an opened to closedtransition (see FIGS. 5A and 5C) the output of one-shot 102 drops tozero volts for a brief period of time before rising once again to 12volts. This rising edge triggers timer 116 (see FIG. 5D) therebyinitiating the fixed time period for timer 116. When timer 116 isengaged in its fixed time period, power is provided to node 117 by wayof pin 3 of timer 116. This provides current to the retractors therebyreleasing them from their engaged position.

When ignition switch 122 is turned on, line 109 is brought to a 12 voltpotential thereby lifting node 117 to that same potential. As long asnode 117 is kept at a 12 volt potential, the seat belt retractors remainin their unlocked position. Soon after the ignition is turned off (seeFIG. 5G) timer 116 is triggered to initiate its fixed time cycle by wayof the input it receives from one-shot 114. During this fixed timecycle, node 117 remains at a 12 volt potential and the seat beltretractors remain in their unlocked position.

One additional advantage of the present invention is the incorporationof a built-in inertia sensor in the L/T circuit 10. As shown in FIG. 3,the gravity sensor 22 is connected to the emitter of Q5. If inertiasensor 22 senses a sudden deceleration or hard cornering it connects theemitter of Q5 to ground thereby locking each of the retractors.

By incorporating a built-in inertia sensor in the L/T circuit 10, a morereliable system is achieved. The system is more reliable because thereare less components to fail. Also, the present invention provides thebenefits of a faster response time and a vehicle component which iseasier to service.

The foregoing detailed description shows that the preferred embodimentsof the present invention are well suited to fulfill the objects of theinvention. It is to be recognized that those skilled in the art may makevarious modifications or additions to the preferred embodiments chosenhere to illustrate the present invention, without departing from thespirit of the present invention. Accordingly, it is to be understoodthat the subject matter sought to be afforded protection hereby shouldbe deemed to extend to the subject matter defined in the appendedclaims, including all fair equivalents thereof.

We claim:
 1. An active seat belt control system for controlling the locking and unlocking of a seat belt retractor in a vehicle comprising:first detection means responsive to the opening and closing of a vehicle door and capable of generating a first output signal indicating the state of said door, second detection means responsive to the on/off state of an ignition switch and capable of generating a second output signal indicating the state of said ignition switch, first control means responsive to said first output signal and said second output signal and capable of generating a third output signal, timer means for starting a timing sequence for a preset time period when triggered by said third output signal, impact sensing means built-in with said control system responsive to a sudden vehicle motion for generating a fourth output signal, and second control means responsive to said third output signal of said timer means, for enabling the unlocking of said seat belt retractor for said preset time period, said second control means also responsive to said fourth output signal for overriding said third output signal and locking said seat belt retractor for the duration of said fourth output signal.
 2. An active seat belt control system according to claim 1, wherein said second control means is connected to said ignition switch and, when said ignition switch is in said on state, said second control means overrides said third output signal and enables said seat belt retractors to remain in an unlocked state.
 3. An active seat belt control system according to claim 1, wherein said impact sensing means is an inertia sensor.
 4. An active seat belt control system according to claim 1, wherein said first detection means comprises at least one detection circuit for detecting the opening and closing state of said vehicle door.
 5. An active seat belt control system according to claim 1, wherein said first control means includes at least one flip-flop integrated circuit chip.
 6. An active seat belt control system according to claim 1, wherein said second control means includes at least one solenoid.
 7. An active seat belt control system according to claim 1, wherein said second control means includes at least one solenoid activated either by output signals from said timer means or by the fourth output signal from said impact sensing means. 